<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>

    <h1 id="showTime"></h1>

    <script>

        var oH1 = document.getElementById('showTime') ;

        // 每隔一秒就计数一次

        var count = 0 ;

        oH1.innerHTML = '我在页面停留了' + count + 's' ;

        setInterval(function () {  
            count++ ;
            // document.write();
            oH1.innerHTML = '我在页面停留了' + count + 's' ;
        } , 1000)

        

    </script>
    
</body>
</html>